金屬在堿液中的應力腐蝕破裂稱堿脆。碳鋼、低合金鋼、不(bu)銹(xiu)鋼等多種金屬材料皆可發生堿脆。碳鋼（含低合金鋼）發生堿脆的趨向見圖8.1.6。輸送NaOH的碳鋼或低合金鋼管道在一定的條件下，能引起碳鋼材料的應力腐蝕開裂（堿脆）。

  由圖8.1.6可(ke)(ke)知，氫氧化(hua)(hua)(hua)鈉(na)濃度(du)(du)在5％以(yi)上(shang)的(de)(de)(de)全部(bu)濃度(du)(du)范圍(wei)(wei)內碳(tan)(tan)鋼(gang)幾乎都可(ke)(ke)能產生(sheng)(sheng)堿(jian)(jian)(jian)(jian)脆(cui)(cui)，堿(jian)(jian)(jian)(jian)脆(cui)(cui)的(de)(de)(de)最低溫(wen)度(du)(du)為(wei)(wei)50℃，所(suo)需堿(jian)(jian)(jian)(jian)液的(de)(de)(de)濃度(du)(du)為(wei)(wei)40％～50％。以(yi)沸點附近的(de)(de)(de)高(gao)溫(wen)區(qu)最易發(fa)生(sheng)(sheng)。裂紋呈晶間型(xing)(xing)。奧氏體(ti)不(bu)(bu)銹(xiu)(xiu)鋼(gang)發(fa)生(sheng)(sheng)堿(jian)(jian)(jian)(jian)脆(cui)(cui)的(de)(de)(de)趨向見圖8.1.7。氫氧化(hua)(hua)(hua)鈉(na)濃度(du)(du)在0.1％以(yi)上(shang)的(de)(de)(de)濃度(du)(du)時(shi)(shi)18-8型(xing)(xing)奧氏體(ti)不(bu)(bu)銹(xiu)(xiu)鋼(gang)即可(ke)(ke)發(fa)生(sheng)(sheng)堿(jian)(jian)(jian)(jian)脆(cui)(cui)。以(yi)氫氧化(hua)(hua)(hua)鈉(na)濃度(du)(du)40％最危險，這時(shi)(shi)發(fa)生(sheng)(sheng)堿(jian)(jian)(jian)(jian)脆(cui)(cui)的(de)(de)(de)溫(wen)度(du)(du)為(wei)(wei)115℃左(zuo)右。超低碳(tan)(tan)不(bu)(bu)銹(xiu)(xiu)鋼(gang)的(de)(de)(de)堿(jian)(jian)(jian)(jian)脆(cui)(cui)裂紋為(wei)(wei)穿(chuan)晶型(xing)(xing)，含(han)碳(tan)(tan)量高(gao)時(shi)(shi)，堿(jian)(jian)(jian)(jian)脆(cui)(cui)裂紋則為(wei)(wei)晶間型(xing)(xing)或混(hun)合(he)型(xing)(xing)。當奧氏體(ti)不(bu)(bu)銹(xiu)(xiu)鋼(gang)中加入2％鉬時(shi)(shi)，則可(ke)(ke)使其堿(jian)(jian)(jian)(jian)脆(cui)(cui)界限(xian)縮小，并向堿(jian)(jian)(jian)(jian)的(de)(de)(de)高(gao)濃度(du)(du)區(qu)域移動。鎳和鎳基合(he)金具有較(jiao)高(gao)的(de)(de)(de)耐應力腐(fu)蝕的(de)(de)(de)性(xing)能，它的(de)(de)(de)堿(jian)(jian)(jian)(jian)脆(cui)(cui)范圍(wei)(wei)變得狹窄，而(er)且位于(yu)高(gao)溫(wen)濃堿(jian)(jian)(jian)(jian)區(qu)。

  一般情(qing)況下，當NaOH濃(nong)度和溫度超(chao)出表(biao)8.1.3的規定時，應對(dui)焊縫（含熱(re)影(ying)響區）進行消(xiao)除應力熱(re)處理。

  表8.1.3 NaOH 濃度和溫度應對焊縫（含熱(re)影響區）進(jin)行消除應力熱(re)處(chu)理的界限

  當NaOH濃度(du)和(he)溫度(du)超(chao)出表8.1.4的規(gui)定時，應(ying)考慮采用含鎳合金。

 碳(tan)鋼(gang)和鎳(nie)合(he)金鋼(gang)在NaOH溶液中(zhong)的應用(yong)范(fan)圍見圖 8.1.8 所示